This invention refers to information display devices, and in particular, to liquid crystal (LC) cells, that can be employed in systems involving optical devices for various purposes, such as planar displays, optical modulators and matrix systems of light modulation.
The known devices of this type usually comprise a flat cell formed by two parallel glass plates with electrodes deposited onto the inner surfaces of the plates. The electrodes are made of a conducting optically transparent material such as tin dioxide. The surface of the plate carrying the electrode is specially treated to ensure the required homogeneous orientation of the molecules of liquid crystal both at the surface and in the bulk of the LC. In a homogeneously oriented layer, the long axes of the liquid crystal near the plate surfaces are aligned parallel to the orientation directions of each of the plates. Usually these orientation directions are perpendicular. After assembling the cell, it is filled with a liquid-crystalline compound to form a 5 to 20 micrometer (mm) thick layer, which is the active medium changing the optical properties (namely, the angle of rotation of the polarization plane) of the cell under the action of an applied electric voltage. This change of optical properties is detected by crossed polarizers that are usually fixed to the external surfaces of the plates. For example see L. K. Vistin, xe2x80x9cApplication of Liquid Crystals in Modern Technologyxe2x80x9d, Journal of All Union Chemical Society, Vol. XXVII, no. 2, (1983), pp. 141-48, which is incorporated by reference herein.
The polarizers employed for this purpose are usually based on polyvinyl alcohol (PVA) films colored by iodine vapors or dichroic dyes; they possess low mechanical strength. Thus special protection measures are required to avoid mechanical damage of the system, making the device more complicated and expensive. As a result, the polarizer can become a complex structure containing up to ten layers:
1. protection film;
2. weak adhesive layer;
3. first carrier film;
4. adhesive layer;
5. polarizing film;
6. adhesive layer;
7. second carrier film;
8. adhesive;
9. silicon compound;
10. release film.
Before attaching the polarizer, the siliconized film (layers 9 and 10) is detached, and after assembling the LC display, the protective film with a weak adhesive layer (layers 1 and 2) can be removed and replaced by a protective glass. As a result, an assembled liquid crystal cell can have more than 20 layers. Note that damage of only one of these layers can make the polarizer inapplicable for use in LC cells. For example see A. E. Perregaux, xe2x80x9cPolarizers for liquid crystal devices: the user""s viewpointxe2x80x9d. SPIE, Vol. 307 Polarizers and Applications, pp. 70-5, (1981), incorporated by reference herein.
One of the ways to protect polarizers from mechanical damage is to place them inside the cell. To this end, the plates carrying deposited transparent electrodes are covered with a polymer (e.g., PVA) solution that may also contain iodine or a dichroic dye. Then the polymer solution is subjected to a shear deformation (e.g., using a squegee moved along the plate surface), upon which the linear polymer molecules are aligned in the direction of squegee motion. After the removal of solvent, the resulting PVA film (containing iodine or a dichroic dye) is oriented and can simultaneously produce both the polarization of light and the alignment of liquid crystal. Then the cell is assembled, filled with a liquid-crystalline compound, and sealed. In this system, the polarizer is inside the cell and is thus protected against the external mechanical factors. For example see U.S. Pat. No. 3,941,901 issued Mar. 2, 1976 to Thomas B. Harsch and incorporated herein by reference.
The main disadvantages of this device are as follows:
(a) Low thermal stability, which is caused by the use of polyvinyl alcohol (or other vinyl polymers) for obtaining the polarizing film, and iodine for dyeing the film;
(b) The use of iodine (soluble in the liquid-crystal medium) for dyeing the polymeric results in gradually decreasing contrast of the pattern and markedly increasing energy consumption, eventually reducing the useful life of the device.
Inventor""s Certificate No. 697,950, xe2x80x9cA Method of Preparing Liquid Crystal Devicesxe2x80x9d, published Nov. 19, 1979, and incorporated herein by reference, shows a system similar to the instant invention in that it is a device, previously known, with polarizers placed inside the LC cell. To create the internal polarizing layer of this previously known device, the inner surface of a plate is coated (above a transparent electrode film) with a dichroic dye gel having a concentration of 1 to 30 weight percent (wt. %). The gel is then mechanically oriented (e.g., by centrifugation), which ensures obtaining a thin dye film of required thickness. After solvent removal, the surface of the plate carries a thin film of a molecularly oriented dye layer, which serves simultaneously as a polarizer and a alignment layer for homogeneously oriented liquid crystal. Therefore, this system, like that described in the aforementioned U.S. Pat. No. 3,941,901, does not require deposition of any additional alignment layers. The plates prepared in this manner are used to assemble a standard LC cell, which is filled with an appropriate liquid-crystalline compound and sealed.
The dichroic dyes are usually represented by compounds of the azoxy group having anisotropic molecules (e.g., chrysophenine, Brilliant Yellow, Direct Blue 14, etc.).
The known LC device of the aforementioned Inventor""s Certificate exhibits higher stability than that reported in the aforementioned U.S. Pat. No. 3,941,901, because the polarizer is formed by a film comprising a dye alone, offering higher thermal stability as compared to that of vinyl polymers.
At the same time, this device also has some disadvantages that restrict the field of possible applications and decrease the useful life. The most noticeable of these are as follows:
(a) Dyes used for creating the polarizing films belong to the class of azo compounds, which have relatively poor thermal and light stability;
(b) Dye solutions used exhibit insufficient wetting of the surface and pronounced viscoelastic rheological properties, which make forming homogeneous polarizing films a quite difficult task;
(c) This LC cell design is characterized by differing surface properties between the materials of transparent electrode and substrate and by a marked relief of the transparent electrode surface, which result in a disorientation of the polarizing coating on the contour boundary of the transparent electrode;
(d) This LC cell design requires placing the reflector on the outer side of the substrate plate in a reflection mode cell, which markedly reduces the advantages achieved by using a cell design with internal polarizing films.
(e) This cell design does not allow creation of an LC cell embodiment employing the supertwist effect.
The purpose of this invention is then to create LC elements with increased performance over previously known LC cells, including LC cells of the reflection type and the LC cells based on the supertwist effect, with the arrangement of all functional optical layers on the inner side of substrates.
The problem formulated above can be solved by implementing one or more of the following ideas:
(a) The internal polarizers are represented by a thin layer of molecular-oriented dichroic dyes forming a polarizing coating;
(b) The polarizing coating is formed from a lyotropic liquid crystalline composition based on organic dyes capable of forming the corresponding LC phase described, (e.g., by formulas I-X) to provide for polarizers with high thermal and light stability;
(c) The reflecting film is formed on the inner surface of the plate;
(d) In the supertwist-nematic cell, the color compensation is achieved by forming a birefringent non-absorbing film with preset optical thickness on the polarizing coating;
(e) Additional protective and leveling layers, are made on the inner surfaces of the plates. 
Besides the dyes, the liquid-crystalline compositions employed for the obtaining of polarizing coatings contain the following components:
(a) a modifying additive to control adhesion of the polarizing coating to the substrate and to produce a plasticizing effect on the coating. This additive can be any of the following types of substances:
low-volatile and high-molecular compounds containing various functional groups (OH, COOH, CONH2, NH, CHO, CO, etc.), for example, pentaerythritol, succinic aldehyde, hydroxycarboxylic acids, poly(ethylene glycol), poly(acrylic acid), poly(acrylamide), poly(ethyleneimine), polyethylene-polyamines, poly(propyleneglycol), their copolymers, etc.;
various lacquers, binders, and glue compositions, including organoelemental ones, such as organosilicon lacquers of the KO grade (where xe2x80x98KOxe2x80x99 is a Russian grade of organosilicon lacquers);
liquid-crystalline polymers, for example, poly(n-benzamide), poly(n-phenylene terephthalimide), and cellulose esters (hydroxypropyl or ethyl derivatives).
(b) A surfactant, which facilitates wetting of the substrate surface;
(c) An antioxidant or inhibitor, which is introduced into the lyotropic liquid-crystalline composition to increase its stability to light and elevated temperature, or to the action of oxidizers, lacquers, and glues.
All the above components allow us to increase both the performance and the working characteristics of polarizing coatings.